2022-06-27 14:10:15 +02:00
|
|
|
the USB bug detector identifies USB type-A cables (or devices) with integrated circuits.
|
2021-07-22 18:13:40 +02:00
|
|
|
|
2022-06-27 14:25:40 +02:00
|
|
|
<img src="picture/v0_front.webp" title="front" height="250"/>
|
|
|
|
<img src="picture/v0_back.webp" title="back" height="250"/>
|
|
|
|
|
2021-07-22 12:22:24 +02:00
|
|
|
usage
|
|
|
|
=====
|
|
|
|
|
2021-07-22 18:13:40 +02:00
|
|
|
to use the USB bug detector, follow the steps provided on the back of the board:
|
|
|
|
|
|
|
|
- insert a CR2025 or CR2032 coin cell battery in the USB bug detector for it to be operational
|
|
|
|
- press on the RESET button to arm the test
|
|
|
|
- the BUGGED LED should be off
|
|
|
|
- plug the USB cable in the USB receptacle
|
|
|
|
- if the BUGGED LED switches on, the USB cable embeds an integrated circuit (e.g. a bug)
|
|
|
|
- if the BUGGED LED remains off, the cable is same to use
|
|
|
|
|
|
|
|
after the test, to save power, press again on the RESET button.
|
|
|
|
|
|
|
|
to ensure that the USB bug detector works, after pressing on the RESET button, press on the TEST button.
|
|
|
|
this will simulate a USB plug with integrated circuit.
|
|
|
|
the BUGGED LED should switch on.
|
|
|
|
this also ensures the battery is not empty.
|
|
|
|
|
2021-07-22 18:35:20 +02:00
|
|
|
when the LED is on, the USB bug detector draws 3 mA.
|
|
|
|
when the LED is off, the USB bug detector draws 64 nA.
|
|
|
|
this results in a idle battery life of 419 years (for a typical 235 mAh CR2032 battery).
|
|
|
|
this is more than the self life of the battery (~ 1%/year).
|
|
|
|
|
2021-07-22 18:13:40 +02:00
|
|
|
fabrication
|
|
|
|
===========
|
|
|
|
|
|
|
|
the board has an optional READY LED (with accompanying resistor located next to it).
|
|
|
|
only populate it to debug the board.
|
|
|
|
the READY LED will we on when the BUGGED LED isn't.
|
|
|
|
this allows to always check if the battery is empty, but this also drains the battery even when not testing because an LED is always on.
|
|
|
|
|
2022-06-27 14:33:03 +02:00
|
|
|
the first prototype of the board (v0) offers three populating options, depending on the available NOR gate part and package:
|
2021-07-22 18:13:40 +02:00
|
|
|
|
|
|
|
- 1x SOIC-14 package: U1+C1
|
|
|
|
- 2x SOT23-5 pachgae: U2+C2, U3+C3
|
|
|
|
- 2x SOT-353 package: U3+C3, U5+C5
|
|
|
|
|
|
|
|
only populate one of the options, depending on the availability of the NOR gate part.
|
|
|
|
note: the Cx decoupling capacitor is not really necessary and is just present for good design.
|
|
|
|
|
|
|
|
mode of operation
|
|
|
|
=================
|
|
|
|
|
2022-06-27 14:33:03 +02:00
|
|
|
an NOR-gate-based SR-latch is used.
|
2021-07-22 18:13:40 +02:00
|
|
|
the RESET button triggers the R signal to reset the latch.
|
|
|
|
when a USB cable is plugged, power is provided by the battery to the cable.
|
|
|
|
if an integrated circuits is present, current will flow through.
|
|
|
|
a 1 k Ohm resistor on the low side (e.g. ground) will create a voltage.
|
|
|
|
if the plug draws more than 1.6 mA, the resulting 1.6 V will trigger the S signal to set the latch.
|
2022-06-27 14:33:03 +02:00
|
|
|
the BUG LED will indicate when the SR-latch is set.
|
2021-07-22 18:13:40 +02:00
|
|
|
the latch remains set until the RESET button is present.
|
|
|
|
thus, even if the plug stops drawing power, the LED remains on.
|
|
|
|
|
|
|
|
this minimum 1.6 mA current draw is often caused by the decoupling/bypass capacitor required by integrated circuit, or accompanying voltage regulator.
|
|
|
|
when charging, the capacitor acts as a short for a small time, allowing current to flow.
|
|
|
|
on USB plugs with just resistors, or LEDs, the resulting current flow is not large enough.
|
|
|
|
|
|
|
|
the TEST circuit simulates an integrated circuit by putting a 100 nF capacitor across the USB receptacle.
|
|
|
|
|
|
|
|
because of the 1 k Ohm inline resistor, and limited 3.3 V provided by the battery, a maximum of 3.3 mA can be drawn by the USB plug.
|
|
|
|
this is often not enough to power up integrated circuit properly, particularly if they use a radio interface.
|
|
|
|
thus it is safe to use the USB bug detector on bugs, without activating it.
|